The invention relates to an injection pump for internal combustion engines. The pump has a pump piston bushing and a pump piston, guided in the bushing, that has control edges for controlling the beginning and end of an injection event. The control edges cooperate with control bores provided in the wall of the pump piston bushing that discharge into a collecting chamber surrounding the pump piston bushing. Fuel can be delivered under pressure into the collecting chamber, and excess fuel, or fuel overflowing at the end of an injection event, can be diverted from the collecting chamber; for the fuel delivery, a suction valve opening to the collecting chamber is connected to the collecting chamber, while for the fuel diversion, a device that affects the flow is connected to the collecting chamber.
When injection pumps are operated at high pressure, corrosion problems due to cavitation phenomena arise upon the diversion to the low-pressure side. When the high-pressure fuel is diverted from the pump chamber to the suction chamber of the injection pump at the instant of the end of supply, pressure fluctuations with high peak values occur. Hollow spaces in the suction chamber resulting from the preceding supply event may implode and cause cavitation damage on the piston circumference, in the control bore and in the suction chamber. The diversion stream also creates secondary hollow spaces in its peripheral and impact zones, which in the ensuing implosion can also cause damage at the aforementioned sites. From Swiss Patent 594 134, it is already known to pump out the diverted fuel, which is returned to the suction chamber, via throttles, in order to attain a pressure increase to a certain extent. The extent of the pressure increase attainable with such provisions is relatively slight, and a decisive advantage cannot be attained unless a suitably high pump pre-pressure is selected. This, in turn, requires a great expenditure of pumping energy and necessitates a correspondingly costly sealing of the pump in the vicinity of the suction chamber.